FRESNO — From an old turkey shed where Dust Bowl migrants once talked in tongues, the Peoples Church has evolved into a powerful institution in the Central Valley. Its 5,000-member congregation, the biggest in this farming heartland, boasts among its members the sheriff, the undersheriff, city councilmen and, if Pastor G. L. Johnson has his way, the next mayor of Fresno.

"Let's congratulate Jim Patterson, one of our fine members," an exultant Johnson said from his pulpit one recent Sunday. He was pointing to the man who handily defeated the incumbent mayor to qualify for a runoff April 27.

"Now that's not politics," he said, smiling as the huge flock of evangelical Protestants smiled with him. "When someone wins something, you should congratulate him."

With his nod of support and much more, this is the first foray into mayoral politics for Johnson and the Peoples Church--dubbed "Heaven on Herndon Avenue" by some. And it has raised delicate questions about the church's clout and whether Patterson, who owns a fundamentalist Christian radio station, would carry the torch of the evangelical right.

"We worry about a hidden agenda," said Rabbi Robert Seigel of Temple Beth Israel, who plans to meet with Patterson in two weeks to voice Jewish concerns. "We're willing to give him the benefit of the doubt. But we're also aware that when some Pentecostals run for office, part of the plan is to deceive."

Patterson, 45, is believed to hold a solid lead over his runoff opponent, Brian Setencich, a 31-year-old city councilman. In a primary field of 13 candidates, Patterson fell 2,400 votes short of winning, with strong backing by major Fresno developers and church brethren who staffed phones, walked precincts and raised cash.

Johnson has hosted spaghetti dinner fund-raisers and browbeat a liberal minister for going public with an alleged anti-Semitic incident that involved Patterson. An ad in the Peoples Church Christmas program solicited $15 campaign donations to attend an open house hosted by Johnson and three other prominent evangelical pastors.

"I've known Jim for 20 years," Johnson, 65, said in an interview. "He's one of our boys. Naturally, you'd like to back him if you can."

Patterson says he is no soldier for the Christian right. His campaign rhetoric leans toward fighting crime and luring industry to Fresno, and avoids any mention of abortion, gays, feminists and other targets of religious right candidates.

Any help he has gotten from Johnson and fellow evangelicals, he said, has more to do with friendship than church mission. "The church and (radio) station are coincidental to my politics," Patterson said. "I see myself as a Jack Kemp conservative."

Fresno is surely a stronghold of evangelical fervor--"born-again" churches outnumber Catholic churches five to one--but the city has not leaned toward a man so God-fearing since an undertaker known for quoting the Bible became the first mayor in 1901.

Like post-World War II Los Angeles, Fresno is caught between its farming past and urban future. With 400,000 residents, it is the sixth-largest city in the state. But the boom years have brought urban sprawl, 18% unemployment and a crime rate second only to Oakland among California's big cities. Voters have never been more restive.

The defeat last month of Mayor Karen Humphrey means the entire seven-member City Council has turned over in two years. Still, it surprised many that Patterson, a first-time candidate, took 47% of the primary vote to Setencich's 32%.

Patterson campaigns on a record of volunteer involvement in secular organizations such as the Fresno Chamber of Commerce, while seldom talking about his roots in the religious right.

His grandfather, a Pentecostal preacher, founded radio stations in Kansas and Colorado. Patterson's father talked of building a fundamentalist Christian broadcasting empire here but lost two radio stations and a TV station to bankruptcy and landed in prison for tax evasion.

Patterson, who had managed one of the stations, bought KIRV radio in 1974 and kept to his father's fundamentalist line. As head of the Fresno Evangelical Political Action Committee in the early 1980s, he lobbied against abortion and gay rights.

In the mid-1980s, Patterson underwent a shift--if not an about-face, certainly a move toward the center. He returned to school and earned a political science degree from Cal State Fresno. He broadened KIRV's format to include programs for Japanese and Hmong residents, and says he had to withstand heat from devoted listeners.

He headed several committees and task forces for the Chamber of Commerce and--rounding out his ecumenical resume--served on the city's human relations commission.

"I got tired of the heavy-handed politics of the religious right," Patterson said in an interview. "I resigned from the National Religious Broadcasters. They had become a carnival sideshow, trinkets for God."